A few types of video transmission systems are commonly used today including multicast, broadcast, and point-to-point video transmission systems. Multicast and broadcast systems both transmit video signals from one source to multiple recipients simultaneously. However, broadcast systems transmit to everyone, whereas multicast systems transmit only to a specific group. In contrast, a point-to-point video transmission system transmits video from one source to one recipient at any given time. A point-to-point video transmission system may have multiple video signal recipients, but this type of system requires multiple video signal transmissions (i.e., one for each recipient).
Video transmission systems are widely used for many purposes. One such purpose is to allow individuals at one or more remote sites to visually and/or audibly participate in a local presentation without physical relocation. In this scenario, the video transmission system typically includes a video source, such as a video camera or computer, at the location at which the live presentation occurs. Also, each participant location is equipped with a video display unit for viewing the presentation. The video signals may then be transmitted from the local presentation site to each participant location using any one of a variety of communication mediums.
One such communication medium is a dedicated line, such as a telephone or cable line. These lines may be provided in a variety of forms including a twisted pair telephone line, a Digital Subscriber Line (“DSL”), an Integrated Services Digital Network (“ISDN”) line, a T1 line, a cable line, etc.
When implementing a video transmission that operates with a dedicated line, the user incurs many costs. First, the system user typically pays an ongoing fee for continued use of the dedicated line. Second, the system user must purchase video transmission system equipment that is compatible with the chosen type of dedicated line. Third, the system user must pay for installation, wiring, and setup of the custom equipment. In addition to the relatively high cost of such systems, the scalability of these systems is limited to those locations to which the dedicated line is connected. In many instances, this may include only two or three locations. For major corporations having hundreds of worldwide offices, employees at non-connected locations will still need to travel to a connected location. Alternatively, dedicated telephone lines may be purchased such that every location is connected to the dedicated line, however, this typically results in tremendous installation and maintenance costs. Consequently, choosing a dedicated line as the communication medium for implementation of a video transmission system having many participant locations is typically cost prohibitive. Also, such systems are typically not compatible with an independent video source that has not been modified or designed for compatibility with the custom equipment.
An alternative communication medium is an existing computer network such as a Local Area Network (“LAN”) or Wide Area Network (“WAN”). Such systems are typically server-based. That is, the same server that controls the flow of all network information also controls the flow of the multicast video signals. Such systems are traditionally more economical than dedicated line systems, as they do not require a dedicated infrastructure. Rather, such systems utilize existing computer network infrastructures, thereby minimizing wiring costs. However, since these systems are server-based, they typically only allow participants to receive multicast video signals via a computer connected to the computer network. In other words, each participant location must be equipped with a video monitor and a networked computer. Furthermore, the video source, such as the computer used to provide the presentation, must also be connected to the network to allow the server to receive the video signals. Additionally, some networked systems require the video source to execute application specific software to allow its video signals to be transmitted via the network. Therefore, although this type of video transmission system may be more economical, it is not compatible with independent, non-networked video sources.
Yet another alternative communication medium is the Internet. Such systems typically require the system user to purchase a subscription from a service provider. This subscription allows the system user to utilize the service provider's server-based infrastructure to manage communications from the system user's computer or video camera to the intended recipients via the Internet. The service provider's infrastructure receives the video signals generated by the system user via the Internet, whereupon the signals are processed and transmitted in a point-to-point manner to each of the designated recipients also via the Internet. Such service providers typically couple the video transmission with a telephone conference call to allow interactive visual and audible presentations. For example, a system user typically schedules a presentation with a service provider to occur at a specific date and time. Thereafter, this information is sent to all intended participants along with password data and information regarding how to connect to the presentation. At the scheduled time, the participants connect to the presentation visually through their computer by logging on to the service provider's web page and entering the required password and/or session information. Similarly, the participants connect to the presentation audibly by dialing a designated telephone number and entering the required password and session data. Such a service typically requires continual payment of a subscription fee and purchase of equipment setup prior to system use. Also, these systems are typically server-based and the service is limited to those features offered by the service provider. Furthermore, these service providers do not offer recording of presentations for later review and/or playback.
Many of the aforementioned communication mediums are digital mediums. When a digital medium is utilized to transmit analog video signals, these analog signals must be converted to a digital format prior to transmission via the digital medium. These digital signals, in uncompressed form, require a communication medium having a large bandwidth (i.e., transmission capacity) if these signals are to be transmitted in near real-time. Generally, even high-speed connections such as cable and DSL are incapable of accommodating such bandwidth requirements. Furthermore, a majority of home users still connect to the Internet via a traditional twisted pair telephone line having even less bandwidth than their high-speed alternatives. Therefore, if a video transmission system is to be compatible with any type of communication medium, the converted digital video signals must be compressed prior to transmission and decompressed after transmission.
The video transmission system of the present invention uses the compression algorithm disclosed in co-pending application Ser. No. 10/233,299, which is incorporated herein by reference, to reduce and compress the digital data that must be transmitted to the remote computers and/or video display devices. Generally, video signals generated by a personal computer have large amounts of both spatial and interframe redundancies. For example, in a near idle personal computer, the only change between successive frames of video might be the blinking of a cursor. Even as a user types a document, a majority of the screen does not change over a period of time. Hence, the compression algorithm used by the present invention takes advantage of these redundancies, both between successive frames of video and within each individual frame, to reduce the amount of digital video signal data that is transmitted to the remote computers and/or video display devices. Reducing the amount of digital data transmitted over the communication medium decreases communication time and decreases the required bandwidth.
Most forms of video compression known in the art require complicated calculations. For example, Moving Pictures Experts Group (“MPEG”) video compression algorithms use the discrete cosine transform as part of its algorithm. Also, the MPEG standard relies on the recognition of “motion” between frames, which requires calculation of motion vectors that describe how portions of the video image have changed over a period of time. Since these algorithms are calculation intensive, they either require relatively expensive hardware that performs such calculations quickly or extended transmission times that allow sufficient time for slower hardware to complete the calculations.
In addition to complexity, many existing video compression techniques are lossy (i.e., they do not transmit all of the video signal information in order to reduce the required bandwidth). Typically, such lossy techniques either reduce the detail of a video image or reduce the number of colors. Although reducing the number of colors could be part of an adequate compression solution for some video transmission system applications, in many other applications, such a result defeats the intended purposes of the video transmission system.
Several patents are directed to the field of video transmission systems. For example, Zhu et al. U.S. Pat. No. 6,567,813 (“Zhu”), assigned on its face to WebEx Communications, Inc., discloses a distributed, collaborative computer system that includes a plurality of server computers connected via a high speed link. The Zhu system allows client computers to connect to any available server computer to start or join a conference hosted on either the server computer to which the client computer is connected or to any other server in the system. This system is server-based, where the server is networked to other servers and clients.
In contrast, Lecourtier et al. U.S. Pat. No. 6,373,850 (“Lecourtier”), assigned on its face to Bull S. A., discloses a videoconferencing system that utilizes a standalone routing switch. The Lecourtier system incorporates at least one group switching center that transmits data directly, in a point-to-point manner, to each data terminal that sends or receives the video and data transmission. According to Lecourtier, this method eliminates collisions between data terminals and thereby allows large quantities of video and audio data to be transmitted over long distances.
Howell U.S. Pat. No. 5,767,897 (“Howell”), assigned on its face to PictureTel Corporation, discloses a video conferencing system that utilizes a director controller situated at the site of the presentation (e.g., on a lecture podium). The director controller includes a video display and a control section. The video display allows the podium speaker to view the transmitted video signals, whereas the control section allows the podium speaker to selectively control the distribution of generated audio and video information signals among local and remote sites. The Howell system incorporates networked controllers having a video camera, microphone, and speaker that captures the podium speaker's presentation and transmits the captured audio and video to remote, networked locations also having a video camera, microphone, speaker, and video display unit.
Yuan et al. U.S. Pat. No. 5,821,986 (“Yuan”), assigned on its face to PictureTel Corporation, discloses a scalable video conferencing system for use between personal computers connected via a network. The Yuan system encodes an image sequence for transmission via the network. The type of encoding disclosed in Yuan enables the image sequence to be decoded at any one of at least two spatial resolutions and at any one of the available frame rates. Such encoding allows video transmission via a network environment in which there is no guaranteed bandwidth or connection quality, such as via standard twisted pair telephone lines.
Salesky et al. U.S. Pat. No. 6,343,313 (“Salesky”), assigned on its face to Pixion, Inc., discloses a computer conferencing system with real-time, multipoint, multi-speed, multi-stream scalability. The Salesky system is a server-based system that allows conference participants to share all or a portion of the video displayed on the participant's computer screen. Furthermore, this system allows conference participants to be located at sites that are remote from each other, and requires all equipment, including the presenter's equipment, to be connected to the same network.
Scherpbier U.S. Pat. No. 6,263,365 (“Scherpbier”), assigned on its face to Raindance Communications, Inc., discloses a browser controller that allows a pilot computer to display selected web pages to both the pilot computer and one or more passenger computers (e.g., to demonstrate and/or discuss selected web page content during a conference call). Initially, the user of the passenger computer is directed to log on to a control web site, which downloads an active control, such as an applet, to the passenger computer. When the pilot computer chooses to display a particular web site to the passenger computers, it sends the web site's URL to the control site, which retrieves and sanitizes (i.e., disables the hyperlinks) the web page. Thereafter, the control site causes the passenger computers' active control to download the sanitized web page. However, the web site viewed by the pilot computer contains active hyperlinks, which the pilot computer user may click to activate. The control site senses these hyperlink selections and causes the pilot computer and passenger computers to be connected to the chosen, hyperlink web site.
Jiang U.S. Pat. No. 6,167,432 (“Jiang”), assigned on its face to WebEx Communications, Inc., discloses a method for creating peer-to-peer connections over a network to facilitate conferencing among network users. The Jiang system allows a designated location (e.g., a web site) on an interconnected network (e.g., the Internet) to be set up such that a conference may be created, and conference participants may be easily joined. The Jiang system maintains the Internet Protocol (“IP”) addresses of the conference participants at the designated location. These addresses are transmitted to new conference participants without requiring that the new conference participants, or their equipment, have prior knowledge of the IP addresses. Once the new participant is joined in the conference, the data packets containing the conference data do not pass through the designated location or a central host, but rather are sent and received directly by the application program of each participant.
Thus, in light of the prior art discussed herein, there is a clear need for a standalone, multicast capable, video transmission system that operates without the need for a service provider and does not rely on a network server or the Internet to control transmission of the video signals. Such a system should provide near real time transmission of compressed video. The video compression must be efficient enough to transmit video in near real-time over standard twisted pair telephone line bandwidths, yet it must not be too lossy (i.e., the transmitted video images must not be noticeably degraded). Further, the video transmission system should be compatible with multiple platforms (e.g. Macintosh, IBM, UNIX, etc.) and should not require any modifications, including connection to a network, to the computer or other video device used for the presentation. Also, the system should not require a client computer at the participants' locations. Finally, the system should have the ability to control all video and data transmissions.